The present invention relates to the production of yarns by the extrusion of filament-forming material, for example, cellulose acetate, through orifices in a spinneret and particularly relates to spinneret orifices of octagonal configuration, the yarn filaments formed by the extrusion of the filament-forming material through the octagonal spinneret orifices, yarn formed of such filaments and methods of producing the filaments using the octagonal spinneret orifices.
Synthetic yarn filaments are traditionally produced by melt, wet or dry spinning techniques, each being very well known in the art. For the production of cellulose acetate filaments, the dry spinning technique has been utilized quite successfully in the past. That is, a solution (usually called a "dope" in art parlance) comprising cellulose acetate and a volatile solvent therefor (usually acetone) is typically extruded through orifices into a gaseous medium which serves to volatilize and evaporate the solvent thereby forming filaments of cellulose acetate. Usually multiple filaments are extruded, gathered into a yarn and the yarn is then wound upon a bobbin. The yarns are then typically woven into fabrics for a variety of textile end uses including garments, draperies and the like.
The spinneret orifices for the production of cellulose acetate filaments have conventionally been of a circular geometry and produce filaments which can be characterized as crenulated or multi-lobal in cross-section. Circular orifices, however, produce a filament which lacks cross-section fidelity, i.e., such filament lacks uniformity of cross-section or periodic smooth surface portions along its length or, conversely, exhibits substantial cross-sectional variance along its length. Finished fabric produced from yarn filaments lacking cross-sectional fidelity appears to have occasional light or dark streaks resulting from differential light scattering. While such fabrics do exhibit a pleasing hand, efforts have been made to improve the fabric produced from such spinnerets. One such effort is disclosed in U.S. Pat. No. 3,839,526. In that patent, yarn filament is formed by extruding filament-forming material through a multi-grooved orifice defined by alternating convexities and concavities along the surface of the spinneret defining the orifice. The yarn filament produced is multi-lobal in cross-section. Various other cross-sectional shapes of yarn filaments, as well as additional characteristics thereof, are also discussed in that patent.
According to one aspect of the present invention, it has been found that there is a relationship between cross-sectional fidelity and the surface area of the filaments throughout their lengths, on the one hand, and the level of air pressure needed for pick insertion in air jet weaving looms, on the other hand. By increasing the number of lobes in the cross-section of the yarn filament and hence its surface area, it has been found that the filaments are more "air-friendly" for use in air jet looms. That is to say, yarn filaments having increased surface area and substantial and consistent uniformity of cross-section throughout their lengths, according to the present invention, afford improved filling performance on air jet looms at lower air consumption rates and hence reduced costs. They also provide a reduced level of fabric defects. Conversely, the yarn filaments hereof contribute to increased fabric production, while maintaining the cost of such production at a relatively constant level. Moreover, this can be achieved without a decrease in hand of the fabric produced by such yarn filaments. The cross-section of the yarn filament can be controlled in accordance with the present invention through appropriate spinneret design with resulting improvements in lowered air consumption and hence cost or increased fabric production in air jet looms and reduced fabric defects.
In accordance with the present invention, spinnerets with octagonally-shaped exit orifices have been found to significantly and consistently provide an increased crenulation level of filaments formed by extrusion of a dope therethrough in comparison with filaments formed by dope extrusion through circular or round spinneret orifices, as well as reduced variability of the cross-section of the yarn filament throughout its length. Both factors significantly improve uniformity of fabric appearance. This is achieved in accordance with the present invention by providing a spinneret orifice having an octagonal shape. That is to say, the present invention provides a spinneret having a plurality of orifices, at least one of which is defined throughout its full perimetrical extent, by eight discrete side edges, each forming an included angle with an adjacent side edge of between 90.degree. and 180.degree.. Preferably, the orifice is formed of a regular octagon.
Also, according to the present invention, a yarn filament is produced having a cross-sectional shape which may be characterized by a pair of generally symmetrical polygonal sub-sections, each having at least three lobes and joined one to the other by a bridging portion extending between adjacent facing sides of the sub-sections. The sub-sections are each generally rectangular in shape and the bridging portion joins the short facing sides of the rectangular sub-sections. By using spinneret orifices of octagonal shape, an average of seven or more crenulations or lobes in the cross-sections of the yarn filaments is produced. Moreover, a substantial uniformity of filament cross-section throughout its length is achieved. Also, a consistency of cross-section among the various filaments produced from the octagonally-shaped orifices is obtained. These achievements result in improved fabric appearance and reduced air pressure requirements on air jet looms.
An additional benefit derived from the use of an octagonal-shaped orifice in a spinneret is the lack of deterioration of the integrity of the octagonal cross-section with time. Historically, one of the problems with spinnerets having orifices of unusual cross-sections has been the tendency for the filament-forming material to deposit in the orifices. This conventionally results in a deterioration of the ability of the orifices to produce a filament having the targeted cross-section. However, tests of the present octagonally-shaped spinneret orifices have demonstrated no substantial cross-sectional deterioration over time. While some deposit of filament forming material does occur over time, it has been surprisingly discovered that such deposits are uniform from one orifice to another in a spinneret having multiple orifices of this invention. In comparison, a spinneret having multiple round orifices typically exhibits nonuniform deposit of filament forming material or preferential depositing of material from one round orifice to another. This nonuniform depositing of material leads to denier per filament (dpf) variability over time. However, use of the octagonal orifices of this invention reduces dpf variability (as compared to round orifices) and, moreover, maintain such low dpf variability substantially constant over time.
According to a further embodiment of the present invention, there is provided a method of forming filaments for the production of yarn by extruding filament forming material through a spinneret having a plurality of orifices including the step of forming the material in at least one of the orifices into a shape having a cross-sectional shape having eight discrete side edges each forming an included angle with an adjacent side edge of between 90.degree. and 180.degree..
Accordingly, it is a primary object of the present invention to provide a spinneret orifice configuration for producing yarn filaments having increased crenulation, hence surface area, improved cross-sectional fidelity and consistency, and, when used in air jet looms, affords improved filling performance characterized by lower air consumption rates or increased loom speed.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, claims and appended drawings.